EARLY in 1814, as Napoleon neared his nemesis, a London musician approached Lord Byron with an extraordinary proposition. Isaac Nathan, 24 or thereabouts, claimed to possess a selection of Hebrew Melodies, "all of them upwards of 1,000 years old and some of them performed by the Antient [sic] Hebrews before the destruction of the temple".

Byron was intrigued. He offered to furnish texts for the sacred tunes and, working closely with Nathan, produced some of his most lustrous verses - including She Walks in Beauty Like the Night and Thy Days Are Done. The Hebrew Melodies enjoyed instant success and remained in print for half a century.

They were, of course, a fraud. The music that Nathan gave to Byron was a jumble of common synagogue hymns, none more than two or three centuries old. In a preface, the composer modified his hype, stating that "the age of these tunes must be left to conjecture". He later emigrated in shady circumstances, reinvented himself as "Father of Australian Music" and sired a line of descendants that includes the eminent conductor Sir Charles Mackerras.

As music teacher to Lady Caroline Lamb, Nathan had approached Byron knowing that it would take a mighty lie to grip his mercurial attention. The poet, prone to anti-Semitic utterances, would have shunned a sheaf of Jewish tunes. But mention of Temple music was another matter. For, to the romantic imagination, music of the Temple amounted to the lost grail, the hidden source of Western harmony. It is a subject I shall be exploring this week at the international summer school and festival at Dartington.

Where does music begin and why does it move us? Biologists suspect that ancient man imitated birdsong, but nothing suggests that these attempts possessed any emotional component. The earliest music with an organised purpose stemmed from man's urge to extol his Creator and attained its musical apotheosis in the 150 Psalms attributed mostly to King David (circa 1000 BC).

These poems were clearly composed with melodies and accompaniment. Changes of mode, tempo and volume are signified textually. David's Psalms formed the core of the choral liturgy in the Temple built by his son, Solomon, and rebuilt after the Babylonian Exile (circa 500 BC).

Their performance grew progressively more sophisticated. The Talmud reports that a person could enter the Temple and know by ear, from the psalmic singing, what day it was, and what time of day, so meticulously shaded were the tunes and tropes. This exquisite culture ended when the Romans destroyed the Second Temple (AD70) and the Jews were dispersed. Not one note of Temple melody, for which there was no system of notation, survived.

Jewish custom prohibits the enjoyment of music during the year of mourning for a close relative. When the Temple was sacked, the mourning was endless. Eleven centuries later, rabbis forbade Jews from hearing instrumental music of any kind until the day of redemption. Yet traces, tantalising wisps of diffused sound, can be inferred. Before the First World War, a Latvian cantor called Abraham Zvi Idelsohn set about studying the liturgy of Yemenite Jews who had been isolated for 1,500 years in hostile Muslim lands.

In their microtonal, monodic singsong, Idelsohn found convincing affinities with Gregorian chant. If this was the oldest authentic Jewish hymnody, Idelsohn argued that the Roman Church must have intentionally adopted Temple music as the basis for its worship - and that the whole of Western music was founded on that source.

The mystique of Temple music was prevalent in early 19th-century Vienna, where Beethoven and Schubert loitered around synagogues to listen to Jews at prayer. Schubert composed the 92nd Psalm in Hebrew. Beethoven interpolated the Jewish Kol Nidrei melody into the adagio of his string quartet, opus 131. Both were seeking a romantic well-spring of music that united all men as brothers.

The counter-romantic impulse, embraced by Richard Wagner, employed music as a token of European supremacy. Wagner's anti-Semitism was not incidental. He proclaimed that Jews were incapable of creative originality, that art was confined to an elite race and that white pagans had all the best tunes. Wagner's pamphlets, which provided cultural legitimacy for Hitler's mania, were a desperate denial of the broad roots of European music, a music that was always more heterogeneous than most Europeans cared to admit.

These roots are now universally acknowledged. The growing appetite for "world music", a genre that includes any blend from Maghreb rap to acid-klezmer, indicates an urge to touch an authentic ethnic past. More than futile arguments over Wagner and his legacy, the modern search for hidden sources amounts to the ultimate defeat of the Wagnerian power-cult.